The present disclosure relates generally to pneumatically actuated valves and more specifically to filters for pneumatically actuated valves.
Pneumatically actuated valves rely on actuators to drive a control element disposed in a flow passage. One widely used example is a butterfly valve, due to their high degree of accuracy, precision, and responsiveness. As is known, one or more actuators drive rotation of a shaft which in turn controls the position of a disc in the main passage. Conventional pneumatic actuators for butterfly valves have a piston defining a supply chamber and a servo chamber, while an intermediate chamber is vented to ambient. Such arrangements usually include a linear actuator and optionally a torque motor servo valve for enhancing responsiveness to commands. Since the actuator relies on pressure differentials of the working fluid in the main passage, it is important that any stray particles or contaminants be removed to the highest practicable extent from the sampled stream(s) before entering the actuator chamber(s) and torque motor(s).
Current filters for butterfly valves are typically constructed of wire mesh or sintered metal screens. For these and other pneumatic applications where space is at a premium, mesh or sintered filters are installed into a bore and configured into a cylindrical or tophat style configuration. A flange forming the “brim” of the tophat is spring-loaded to seat the filter and hold it in place.
While generally effective, this configuration can face limits on filtration capacity at the small diameters typical of such applications. Mesh and screen filters also can face effective limits on micron rating based on a desired replacement or maintenance interval. Smaller holes increase the time before the filter is clogged, reducing its effectiveness. Further, when clogged, the mesh and screen filters lift against the spring load holding it in place, allowing particles to completely bypass the filter and enter the actuator and/or torque motor.